<!doctype html>
<html lang="zn-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
</head>
<body>
<button id="in">fadein</button>
<button id="out">fadeout</button>
<button id="toggle">fadetoggle</button>
<button id="to">fadeTo</button>
<div id="div1" style="width: 80px;height: 80px;background-color: aqua;display: none;"></div>
<div id="div2" style="width: 80px;height: 80px;background-color: #99ffbc;display: none;"></div>
<div id="div3" style="width: 80px;height: 80px;background-color: #ffc39d;display: none;"></div>
<script src="js/demo2.js"></script>
</body>
</html>